Phase comparison system



Sep@o 17, 194e; M FUCHS 2,407,659

PHASE COMPARISON SYSTEM l Filed Feb. 17, 1945 26 I9 ff" 5g-Pansa? 7 "P//Asfk' 55 59* "-4056 'an INVENTOIL Mo/Pro/v fac/fs Patented Sept. 17, 1946 UNITED STATES PAT-ENT OFFICE PHASE COMPARISON SYSTEM MortonvFuchs, NewYork, Y., `assignorfto Federal Telephone vand Radio Corporation, New York, N. Y., a corporation of Delaware Application February 17, 1945, Serial No. 578;'191

(c1. Au-.11)

12 Claims. l This invention 'relates to phase-comparison systems, particularly those adapted to be used for direction finding purposes. y ,In directionally shiftable radiant acting systems, used either as direction finders or as rotary beacons, systems have been proposed wherein the directive pattern is shifted through a predetermined angular relationship by means of a phase shifting network shifting the phase relationship of two or more vradiant acting means with respect to a given translating device, such as a transmitter or a receiver. In certain of such systems, transmission lines (usually articial) are coupled toantennas, and the direction finding receiver is coupled to said transmission lines at continuously. shifting points along said lines to produce effective shifting of the phase and consequently of the radiant action patterns of said antennas without requiring physical movement thereof.

An object of the present invention is the provision of an improved shiftable radiant acting system, such as for example of the types hereinabove described.

When such systems are used in direction nders they require an excellent match between the vphase shifting transmission lines and their terminations in order to obtain an electrically flat line along which the phase varies linearly. When the antennas coupled to the said lines also serve as terminating impedances, it becomes necessary to match the antennas with the lines. A system of this type is described in the copending vapplication of N. Marchand, Serial No. 553,562, filed September 1l, 1944. .Another object of the present invention isa provision of an improved phase comparison direction finding system in which the antennas do not have to match the transmission lines.

Another object of the present invention is the provision of an improved phase comparison direction finding system which uses matching resistive loads to terminate the transmission lines.

Phase comparison direction finders using matching resistive loads to terminate the transmission lines Vhave not heretofore proven satisfactory. Direction indications have been obscure and inaccurate. I have discovered this to be .due to the fact that the direction finding receiver draws current from the transmission lines.

This alters the impedance of the lines, causing a mismatch and producing reflections and standing Waves. It also unbalances the lines in relation to each other. Consequently, instead of a linear shift of phase along the lines, the phase shift becomes erratic and uncontrollable and it becomes impossible to correlate andsynchronize the indicating device of the direction finding receiver with the consequently irregular shifting ofthe maximum or null of the resulting radiant action pattern. Y I n v Another object of the present invention'is the provision of a -phase comparison direction findingH-systemusing matched resistive load termi-- nations for the transmission Ylines along which lines coupling of the receiver to successive vpoints produces corresponding shifts in directions of the nulls ofthe radiant action patterns.

Ideally the foregoing object is accomplished, according to my invention, by having the means coupling the transmission lines to the Vdirection nding receiver oier infinite impedance to current from said lines at the-nulls, that is, when the voltagesat the coupling points of each of the transmission lines are in phase and equal. Under null conditions no current will be drawn from the lines, the lines remain at and the null points onthe line are accurately and regularly spaced and clear.

I When such voltages are unequal and/or out of phase said'means preferably olers moderate resistive impedance and good power transfer. Under this'condition the flow of current from the' transmission line to the direction finding receiver both mismatches and unbalanoes the transmission lines of the system. While this affects the rest of the radiation pattern, it is unimportant when the null is being used to determine direction. While the conditions described above are ideal, satisfactory results are obtained when said conditions are only approximated. When the voltages are in phase and equal it is sufficient if the impedance of the coupling means be relatively great compared with that of the transmission lines. When the voltages are not in phase it is desirable that the impedance of the coupling means become less.

Another object of the present invention is the provision in such a system of receiver coupling means which present an impedance large in relation to the impedance of the transmission lines when the voltages at the coupling points are in arpredetermined phase and amplitude relationship 'and which present lesser impedances when said voltages diner from said phase relationship.

According to a feature of my invention I connect two spaced antenna units to one end respectively of two separate transmission lines kand terminate the other ends of said lines in matching resistive impedances. The transmission lines are plished by providing phasers intermediate the f antennas and the transmission lines coupled to.

the translating apparatus.

In accordance with my invention I interpose a circuit means between the translating apparatus and the transmission lines whose impedance varies in accordance with the voltage conditions prevailing at the coupling points on said transmission lines. When said voltages are of a predetermined phase and amplitude relationship the impedance of said circuit means is relatively great compared to the impedance of the transmission lines. this phase relationship said impedance is less. In the output of the translator arrangement an indicator may be provided producing a trace line positioned in accordance with the positioning of the phase control means. The output energy from the translating device may be applied to the indicator to produce deection of theftrace in accordance with the strength of the signals. The phase shifting is preferably made to occur in the form of a sine wave so that directional shifting of the radiant action pattern isy made at a uniform rate and the indicator calibration may then be made of a uniform or straight line scale and will remain in proper calibration for all received frequencies.

In the system hereinabove described it is'not necessary that the impedances of the antennas match the impedances of the transmission lines. Because of the relatively high impedance of the circuit means when the voltages at the coupling points are at a predetermined amplitude and phase relationship, at such phase relationship relatively little current will flow from the transmission lines and since said transmission lines are terminated in matching resistive impedances said lines will be flat and consequently said phase relationship will occur at predetermined points on the transmission lines bearing a xed relationship to the direction of the null of the radiant action pattern of the antennas. Thus accurate directional indications will be obtained on the indicator.

A better understanding of my invention and the objects and features thereof may be had from the following particular description thereof made with reference to the accompanying drawing in which:

Fig. 1 is a block diagram of a simple direction finding receiver unit operating in accordance with the principles of my invention.

Fig. 2 is a modified arrangement of the'direction finding receiver unit illustrated in Fig. 1.

Turning first to Fig. 1, two vradiant energy means, for example antennas I and 2 are separated a given distance preferably less than 180 electrical degrees. Antennas I and 2 are coupled by any suitable means to ends 3 andI `4 respectively of transmission lines and 6. Said transmission lines 5 and 6 may beicomprised entirely of regular transmission lines or may each consist in part of a transmission line and in part of articial transmission lines 'I and 8 respectively. The other ends 9 and ID of transmission lines v5 and 6 are each connected in series with When said voltages differ fromy one of two matching resistive impedances I I and I2 which latter` are in turn connected to ground. Since the sharpest indication of direction is produced by a null indication I arrange the lines in the manner indicated in the drawing so that at the midpoints of artiiicial lines l and 8 there will normally be a zero or null providing the signal is approaching at right angles to the plane delined by the antenna systems. If the energy arrives at some other angle, so that antennas I and 2 are not energized in phase, the null will and I4 are Yarranged to move together alongY their respective articial lines and are coupled to said lines. Artificial lines I and 8 are preferably made electrically equal to the spacing between antennas I and 2 so that a complete effective rotation of the directive action of the system may be obtained. Contacts I3 and I4 are connected over coupling lines I5 and I6 respectively to a circuit means I'I, hereinafter described, which in turn is connected to a receiver I8 in the output of which is provided an indicator I9. Preferably, indicator I9 is some form of visual indicator arrangement such as a cathode ray tube 20 provided with deecting means such as a coil 2|. Drive means 22, which may for example be a motor, is coupled over a shaft 23 to a driving wheel 24 and over a shaft 25 to a control means indicated by arrow 26 for rotating deflection coil means 2I about the cathode ray tube 20. Mounted on wheel 24 is crank 21 which serves during rotation of wheel 24 to shift contacts I3 and I4 regularly backward and forward along artificial lines I and 8 respectively. If drive means V22.' operates continuously at a given speed, contacts I3 and I4 will travel back and forth along their respective articial lines at a speed corresponding to a simple harmonic motion or sinusoidally. Accordingly, the phase angle of the energy transferred from antennas I and 2 to the receiver I8 wil] continuously be varied providing the phase shift along the artificial lines is regular, which in turn depends on the lines being relectrically flat. Assuming for the moment that the lines are flat, the aforementioned operation -will provide an output in the form of a sine wave' so that effective regular rotation of the directive action of the pattern from antennas I and 2 will thus be effected. Since coil 2I rotates in synchronism with the movement of contacts I3 and I4, radial deflection of the cathode ray beam will be made in accordance with the incoming signal energy so that a pattern 28 dependent upon the direction of a transmission station will be traced on the screen of the cathode ray tube. Since the displacement is linear upon the cathode ray screen a'permanent calibration may be provided. With the relationship outlined, indications will be uniform for all frequencies received.

In systems of the type described the instantaneous angular position of the trace in cathode ray tube 2li corresponds to a given position of contacts I3 and I4 along articial lines I and 8 respectively. Likewise,'providing the artificial lines are electrically flat, the instantaneous position of contacts I3 and I4 would correspond with a given direction of the resultant radiant action pattern. Under such conditions rotation of driving wheel 24 would correspondingly rotate the trace of cathode ray tube 20 and the radiant acmonete tion pattern, thusenabling 'obtainingof--accura'te 'direction alindications.

`Sincethe present direction liinding Ireceiver-is of the null Vtype it is primarily the 'directi'on'of the null-of the directional npattern and not the position ofthe vrest 'of said Apattern which must correspond with given Ypositions of contacts I3 and "14.

If 'artificial lines I 'and 8 "are velectrically `flat and energy is received iromfa given'dire'ction at a given point `along 'arti'ciallines Tand '8, voltages appear equal Ivin famplitude :and "corresponding jin phase. Said pointis herein termed a vnull point. If the lines remain iiatan'd thed-irection from #which energy is received is varied, 't'.ln'eniill point =wi1leorrespondingly vary. As will 'be Aapparent however, if said lines vare 'not at "the direction-of lthe null will not-correspond vtzr-'any given position of the contacts `I'3 and t4 because of the eiifect of the standing lwaves lwhich will alter 4the phase shift along said lines. As has .been stated hereinbeiore the lineslose 'their filatness when current is -drawn'from said Vlinesby thereceiver.

v.Inv accordance with my invention 'circuit means Il'I are-adapted to prevent the drawing of any vsubstantial amount of current by the `receiver when* contacts I'3 and I4 are at a null 'pointgthat is, when the voltagesat agiven'point on arti-licial lines 'Iland are equalan'd in phase.

`This is accomplished 'by arranging coupling lines I5 and I6 each in series -with coils 29 and 3D respectively of circuit means I"I. Coils 29 vvand 30 may be-arranged on a single form with or without a core of magnetic material depending :on the 'frequencies involved. Coils 29 and 30 are as closely Vcoupled as possible and are arranged so that when voltagesequal'and `in phase,

appear vat contacts I3 and I4, the resultant =cur y rents owin-g through coils 29 'and 3D produce fields in said V'coils reenforcing each other. Thus the e'iective inductance of 'each of said coils is increased, thereby increasing the effective 'impedance of said coils. Coils 29 y and 3i! are provided with 'a sufficient lnumber' of 'turns so `that 'the resultant imped'ance's under such conditions are sufficient to prevent receiver IIB from drawing any substantialamount o'f current fromar'tiicial lines y1 'and 8 and consequently said lines 'are then substantially electrically hat.

From the foregoing it will bev seen that "for :any

given direction from which energy "is received vvthe' artificial lines will become ilat when contacts I3 and I4 reach a point corresponding '.t'o the null. Thus the indication of the null on cathode ray tube will correspond with `a given direction from which energy is being received.

Circuit means I'I will obviously oier less -impedance to the transfer of energy between articial lines I and 8 when the voltages at contacts `I-'3 and Ill are out of phase since the resultant current flow through coils`29 and 30 will not produce fields Aof the same :magnitude 1asare produced under null conditions. Consequently the transfer of current from artificial lines 'I and 8 will in all probability set up 'standing waves on Isaid lines at other than the null points, but since the null is being used for direction indications this vfact does not interfere with accurate voperation ofthe system.

Referring now to Fig. 2, another system lenibodying my invention is there disclosed. The antenna elements may consist of dipoles `3'I 'and 32 which are coupled to variable phasers of 'any suitable typev 33 and 34 respectively. Said phasers are in turn connected to Jtransmission lines 35 land 36 Which-terminate 'in matching resistive limped'aneesS'I and Tillrespectively. 'One endlo'f thelimpedanc'es 3'I vand -3'8 is coupled by means loi Elines 39L and 4U Vtof-circuitv means Ir'I 'similarto 4that described in connection witli'Fig. 3l, circuit means If'I bein'gin turn'connec-ted to re- 'ceiver ll8 whose output is applied tolindicator Il!) of l`cathode ray tube `ZI). lDeiieoting *coil 2fI -of tube 2D is driven -by-a driving means AvIII JAwhich also synchronously :varies phasers '33 and 34. Operation of i'the driving means `changes the phase "of the voltages lap'p'earing l on lines 39- and 40 in rela-tion'fto antennas 3l an'd3`2iand v'consequently rotates 'the Anull of the radiant 'action pattern of saidantennas. `lAt theesa'metpimedriving means 4I, rotating 'deflection coil V2|, -vthereby 'correspondingly '-r6tates the -trace off-:cathode ray tube 20. -=`A tra'cell-'Z-'such asilllustrate'd Amay be produced, Withthe point '43"=tliereof,produced in response gvto equal fand in 'phase voltages at lines 39 and r411 and corresponding'tod-theiiiiill, indicating the 4direction from 'which energy fis being received.

While 'Ilhave ldescribed the details of ftwofembodiments of my VVi-n-wention Y.it is to be under- 'Stoo'd 'that 'variations inlay be made inisuch deltails as will be apparent to 'those versed yin the art vwithout departing from'theiteachings thereof. For example, various different Yof .antennas 'and .drivinglmeansmay b'e employed. Moreover, While `my iinvention `is "particu-larly :adapted for use -in "phase c'onniarison `direction finders, the principles lthereof lmay y,be applied `to .priivid'e phase comparison indications :for 'otherlpurposes While I have 'shown one circuit means, namely the coupled coils 29 :and 30 which are adapted to present maximum Limpedance to currents resulting from'equal and 1in phase voltages, it is'to be understood that `other devices for this purpose may fbe employed. "Instead of contacts I3 and yIIL-.other coupling means, such as-capacitivecoupling, maybe employed. Therefore lits-hould be distinctly understood `that these illustrations of my invention are 4given 'merely `by Way, of example Tand Inot as fa :limitation von myj invention as Yset `forth in Ythe -objects thereof and the aecompanyingc'laims.

What -is `claimed is:

l. fA-system -for comparing the varying phase vof 'voltages vpresen-t 'on respective transmission lines said lines termina-ting in their character- "istie impedances, comprising, -a translating de- -v-ice, :circuit means coupling said transmission lines to said device, said vcircuit means-.havingl an input impedance relatively large 'compa-red tothe transmission line impedance to voltages having a `predetermined amplitude and phaserelationship Yat the -points -at which said'circ-uit means lis coupled to the transmission lines and having a llesser input impedance to voltages -at saidpoints differing from said predetermined'phase relationship, and means for variably controlling the lplaise of energy transierred'between said lines-and said circuit means.

2. -A system according to claim l, wherein the said coupling means includes a. pair of closely -coupledcoils serially connected respectively `with said transmission lines aand providing reinforcing ii'e'lds iin response to equal iin phase voltages in said transmission lines.

3. .A system for indicating the relative phase of `energy in two sources comprising a translating device, 'means `for coupling said sources to said translating 'device comprisinga `pair of 'transmise sion lines each coupled to one of said sources, matching impedances terminating each of said transmission lines, circuit means coupling said transmission lines to said device, said circuit means having an input impedance relatively large compared to the transmission line impedance to voltages having a predetermined amplitude and phase relationship at the points at which said circuit means is coupled to the transmission lines and having a lesser-input impedance to voltages at saidA points diering from said predetermined phase relationship, and means for variably controlling the phase of energy transferred between said circuit means and said two sources.

4. In a directional shiftable radiant vacting system including two spaced radiant acting means and a radiant energy translating device, means for coupling said radiant acting means to said radiant energy translating device comprising a pair of transmission lines each coupled to one of said radiant acting means, matchingv resistive impedances terminating each of said transmission lines, said transmission-lines having a given impedance, circuit means coupling said transmission lines to said device, said circuit means having an input impedance relatively large compared to the transmission line impedance to voltages having a predetermined amplitude and phase relationship at the points at which said circuit means is vcoupled to the transmission lines and having alesser input impedance to voltages at said .points differing from-said predetermined phase relationship; and means for variably controlling the phase of energy transferred between said circuit means and said two radiant acting means.

5. In a directional shiftable radiant acting system including two spaced radiant acting means and a radiant energy translating device, means for coupling said radiant acting means t said radiant energy translating device comprising a pair of transmission lines each coupled to one of said radiant acting means, matching impedances terminating each of said transmission lines, said transmission lines having a given impedance, circuit means coupling said transmission lines to said device, said circuit means having an input impedance relatively large compared to the transmission line impedance with respect to equal, in phase voltages at the points at which said circuit means is coupled to the transmission lines v and having a lesser input impedance With-respect to voltages of equal amplitude which are out of phase, vand means for variably controlling the phase of energy transferred between said circuit means and said two radiant acting means.

6. The system according to claim wherein said circuit means includes a pair of closely coupled coils eachbeingarranged in series between saidtranslating device and one of said transmission lines,`said coils being arranged to produce reen'forcingy iields in response to said equal, in phase voltages. Y

7. In a-directional shiftable radiant'acting sy'stem including two spaced radiant acting means and a radiant energy translating device, means for coupling said radiant acting means to said radiant energy translating device comprising a pair of-transmission lines each coupled to one 0f said lradiant acting means matching impedances terminating each of said transmission lines, said transmission lines having a vgiven impedance, circuit means, coupled to said translating device, and means continuously variably coupling said circuit means to said. v.transmission lines along diiferent points thereof to couple said translating device in variable phase with respect to said two radiant acting means, said circuit means having an input impedance relatively large compared to the transmission line impedance with respect to voltages having a predetermined amplitude and phase relationship at thepoints at which said circuit means is coupled to the transmission lines and having a lesser input impedance with respect to voltages diifering from said predetermined phase relationship.

8. The system according to claim 5 wherein said circuit means includes a pair of closely coupled coils each having arranged in series between said translatingdevice and one of said transmission lines, said coils being arranged to produce reenforcing fields in response to said voltages having said predetermined amplitude and phase relationship.

9. A radio direction finder system comprising two space antenna means, a pair of transmission lines each .coupledat one end thereof to one of said antenna means, a pair of matching impedances each terminating one of the other ends of said transmission lines, a radio receiver means, circuit means coupled to the input of said receiver means, means continuously variably coupling said circuit means to said transmission lines along different points thereof to couple said receiver in variable phase relationship with respect to said two antenna means, and indicator means coupled to the output of said receiver means, means for producing a trace line on said indicator means in accordance with the phasing between said receiver means and said two antenna means, and means for deiiecting said trace line in response to energy received in said receiver means, said circuit means having an input impedance relatively large compared to the transmission line impedance with respect to equal, in phase voltages l at the points at which said circuit means is coupled to the transmission lines and having a receiver input impedance with respect to other phase relationships of said voltages, said indicator means being arranged to produce a directional indication inresponse to equal,.in phase voltages at said coupling points.

10. A direction finding system according to claim 9, wherein said circuit means includes a pair of closely coupled coils each being arranged in -series between said receiver means and one of said transmission lines, said coils being arranged-to produce -reenforcing elds in response to said equal, in phase voltages. i Y

11. In a directional shiftable radiant acting system including two spaced radiant acting means and a radiant energy translating device, means for coupling said radiant acting means to said radiant energy translating device comprising two phase control means each coupled to one of said radiant acting means, a pair of matching impedance means, a pair of transmission lines each having one end thereof coupled to one of said phase-control means and the other end thereof terminating in one of said impedance transmission lines having a given impedance, circuit means coupling said transmission lines to said device, said circuit means having an input impedance relatively large compared to the transmission line impedance with respect to equal, in phase voltages at the points at which said circuit means is coupled to the transmission lines and a lesser input impedance with respect to said voltages in outer phase relation and means for simultaneously controlling both said phase control means to vary the phase relation of the translating device in relation to both said radiant acting means.

12. In a radio direction nder system including two spaced radiant acting means and a direction finding receiver means to said radiant acting means comprising two phase control means each coupled to one of said radiant acting means, a pair oi resistive impedance means, a pair of transmission lines each having one end thereof coupled to one of said phase control means and the other end thereof terminating in one of said impedance means, said transmission lines having a given impedance, circuit means coupling said transmission lnes to said receiver means, said circuit means having an input impedance relatively large compared to the transmission line impedance With respect to equal, in phase voltages at the points at which said circuit means is coupled to the transmission lines and having a lesser input impedance with respect to said voltages out of phase, means for simultaneously controlling both said phase control means to vary the phase relation of the receiver means to both said radiant acting means, and an indicator coupled to the output of said receiver and ar ranged to produce an indication in response to said equal, in phase voltages.

MORTON FUCHS. 

